Interpretive Summary: The greenbug is the most important pest insect of wheat in much of the Great Plains region of the United States. The parasitoid Lysiphlebus testaceipes is the most important biocontrol agent of the greenbug. This parasitoid is sometimes, and in some geographical areas, effective at maintaining greenbug infestations below economically damaging levels; at other times and in other places, it is ineffective. It is important to understand as much as possible about the parasitoid's biology so that we can develop ways to increase its effectiveness and predict when and where it will effectively control greenbugs. The purpose of this study was to determine how varying temperatures affected the development and survival of L. testaceipes from different geographical areas of the Great Plains, using greenbugs as a host. The number of days required for development, survival, and female-to-male ratio were studied at five constant temperatures for colonies of the parasitoid that were collected in south Texas, central Oklahoma, and central Nebraska. Temperature affected all aspects of development and sex ratio equally for colonies from the three locations. However, survival to adulthood was greater at low temperatures (10 deg C) for the Nebraska colony, suggesting that there may be geographical variation in the ability of L. testaceipes populations to survive cold temperatures. Because greenbugs survive well at temperatures of 10 deg C and below, low temperatures (near freezing) during winter could limit the effectiveness of L. testaceipes as a biocontrol agent in some geographical areas in the Great Plains.

Technical Abstract: Using greenbugs, Schizaphis graminum (Rondani) as a host, the number of days required for development, survival, and female-to-male ratio were studied at five constant temperatures (10, 14, 18, 22, and 26 deg C) for colonies of Lysiphlebus testaceipes (Cresson) that were collected in south Texas, central Oklahoma, and central Nebraska. Developmental rate and lower rdevelopment threshold were described by a linear function and compared among wasp colonies. The temperature thresholds for development from egg to adult for the Nebraska, Oklahoma, and Texas wasp colonies were estimated to be 5.64, 6.61, and 6.42 deg C, respectively; corresponding degree-day requirements for development were 181.2, 169.5, and 188.0 degree-days respectively. No differences in developmental rate or lower development threshold estimates were observed among the wasp colonies. However, adult survival at 10 deg C was greater in the Nebraska colony, suggesting that there may be variation in the ability of L. testaceipes populations to tolerate and survive cold temperatures.